1. Propylene Oxide Unit
Propylene oxide production = 29,000 MT/PA
Side products:
Dichloropropane, Dichloroisopropylether, Dipropylene glycol,
TPG residue.
Utilities used:
MP Steam, LP steam, LP condensate, Cooling water, Chilled
water, Raw water, Demineralised Water, Process water, soft water,
Inert gas, Instrumentation Air, Plant Air, Electricity.
Process Description:
PO is obtained by saponification of the propylenic chlorhydrin
with lime then recovered by distillation. This production way is
particularly well suited to small and medium size units.

2. Stages for the process are:
-Chlorhydrin production
- Recycle gas washing & cooling
- Purge gas treatment
-Saponification
-Purification of PO
-Purification of Dichloropropane(DCP)
Chlorhydrin Production:
Reaction Section:
Chlorine and propylene are fed at the bottom of the reactor.
Propylene was added above 5 mts. from chlorine in order to have
complete dissolution of chlorine and to avoid chlorine, propylene
reaction in gaseous phase. Chlorohydrin flows to saponifier buffer
tank. Excess propylene, Inerts, DCP leave the reactor at the top are
washed using water to absorb chlorine, Hcl.
Cl2 + H2O  ClH + ClOH(Hypochlorous acid)
ClOH + C3H6(Propylene)  ClC3H6OH(Chlorhydrin)
DCP is formed by
C3H6 + Cl2 = C3H6Cl2

3. And Dichloroisopropyl-ether(DCIPE) according to,
C3H6 + ClOH + ClC3H6OH  (C3H6Cl)2O + H2O
The reaction is slightly exothermic and takes place in aqueous
solution.
Direct contact of propylene and chlorine produces DCP hence first
total dissolution of chlorine is performed before propylene is injected.
DCP solubility in water or in chlorhydrin solution is very low, and if
chlorine and propylene react in DCP phase they produce mainly DCP.
DCP phase appearance can be reduced by using excess propylene.
The DCP is removed by stripping by propylene. It is also avoided by
using diluted solution.
DCIPE formation is less important compared to DCP formation.
For DCP stripping, temperature of reactor is maintained as high as
possible. But solubility of propylene at in chlorhydrin solution is
greater at lower temperature and also chlorhydrin solution is more
corrosive at high temperatures.
So in practice, reactor temperature is kept between 500 and 600 C as at
temperature over this, chlorhydrin yield is decreasing and biproducts
yield is increasing.

4. Recycle Gas washing & cooling:
Caustic soda used to condense DCP, Neutralize acid and cools the
gas. 12.5% NaoH was used (soft water+ 50% NaoH). The overhead
product from Recycle washing column was sent to the Liquid KO
drum. The bottom product from washing column was sent to Soda
decanter. The output from Soda Decanter was sent to First DCP
Decanter column.
Purge Gas treatment:
The purge gas along with DCP was sent to Activated charcoal Gas
treatment (L0101). Adsorption of purge gas in charcoal takes place.
The purge gas was sent as boiler feed treatment. DCP from Activated
charcoal was sent to the DCP decanter for DCP storage. Regeneration
of Activated charcoal was saturated with propylene continuously.
Saponification of Chlorhydrin:
Using Saponifier column. It contains 6 sieve trays at upper part and
8 sieve trays at lower part.
2ClC3H6OH + Ca(OH)2  2C3H6O + CaCl2 + 2H2O
Sufficient alkali must be added to saponifier to neutralize HCl formed
in the chlorhydrin reactor and also to hydrolyse chlorhydrin to
propylene oxide. A 15 to 20 wt% lime is used. An excess of 10% of

5. lime is used so the concentration of OH ion remains constant
throughout the course of the reaction.
The rate of solution of lime is in fact the rate limiting step of the
reaction.
Saponifier is also a stripper for PO, stripping is obtained by steam
injection.
The reaction must be completed rapidly to avoid excessive stripping
of unreacted chlorhydrin and a high yield loss as propylene glycol.
Removal of PO by stripping from solution must be done quickly to
drive equilibrium to right and to minimize formation of PG. The
bottom product from saponifier was sent to waste water flash drum.
The top product from saponifier was sent to PO distillation Column
Purification of PO:
PO Dsitillation column was used to obtain the pure PO product in
addition PO stripping column was used.
PO distillation coumn PO Reflux drumPO stripper
PO extracted from stripping from the saponifier contains water,
DCP, DCIPE and other impurities as aldehydes. It is sent to the
distillation column in which aldehydes are dimerized by injection of
caustic soda solution as catalyst.
PO is recovered from the top of the column and condensed, it is
sent to a stripping column in which the lights are separated.